In the transportation and storage of materials such as chemicals, paints and toxic liquids, that may be both valuable and hazardous, it is imperative that the sealed integrity of a container be maintained. For example, the sealing cover or lid for a cylindrical paint container must be retained in sealing engagement with the container to avoid the loss of an investment, to prevent the inconvenience and expense of a clean-up, and, in some cases, to protect the environment and satisfy regulatory requirements. Measures must sometimes be adopted to prevent the loss of a seal and subsequent spillage that might otherwise be caused by the presence of an elevated relative pressure within a container. Elevated internal pressure or a pressure differential between the interior and exterior of a container can be associated with, for example, impact, indentation of the container, elevated temperatures, lengthy storage times, vibratory agitations, liquid vaporizations, chemical reactions, and altitude changes in transportation and storage.
The United Nations Committee on the transportation of dangerous goods prescribes certain regulations that provide common and uniform measuring systems for specifying packaging and container requirements to be applied internationally. In general such requirements differ from existing U.S. governmental regulations in that they are directed to container performance rather than to the specific type of materials used in the construction of a container. Such regulations include performance tests having to do with internal pressures of containers, such as cylindrical metal paint cans having removable friction locked lids or covers. In brief, these tests require a water-filled container with a cover in place to be subjected to predetermined internal pressures for specific testing durations. No leakage may occur during a test in order for the container to pass inspection and approval. In the case of a multi-friction fit paint container or its equivalent, the sealed container must withstand an internal pressure of 14.5 pounds per square-inch (psi), also approximately 100 Kilopascal, relative to the pressure of the exterior of the container, for a period of five minutes. A typical multi-friction fit container is not engineered to be a pressure vessel, and, without some modification, it will not generally comply with the United Nations test regulations.
A need therefore exists for an improved device that maintains the sealing engagement of a cover with a container. A need exists for such a device that retains a cover with a container subjected to a range of relative pressures within the container. The present invention meets these and other needs, as described hereinafter.